


How to Safely Cancel Boost.Asio\'s basic_waitable_timer and Prevent Unexpected Behavior?
Oct 25, 2024 am 10:21 AMCancelling Deadline Timers Safely in Boost.Asio
Boost.Asio's basic_waitable_timer enables the scheduling of asynchronous timeouts. While it provides a cancel() method to cancel a pending operation, safe cancellation requires careful handling to prevent unexpected behavior.
The Problem: Non-Robust Cancellation
In the provided code, cancellation via the post() function doesn't always work as expected. The timer keeps starting new operations even after a cancellation attempt. This occurs because the cancel() call only cancels asynchronous operations that are currently in flight. If the timer expires before the cancellation is invoked, subsequent calls to async_wait() will continue as normal.
Diagnosing the Issue: Handler Tracking
To understand the problem, handler tracking can be enabled to visualize the flow of events. By inspecting the resulting trace, it becomes apparent that the cancellation attempt is executed after the timer has already expired, resulting in the subsequent operations being unaffected.
Detecting Expired Timers
To detect expired timers before cancellation, the following approach can be used:
- Check the expiration timepoint of the timer.
- If the timepoint is set to a specific "invalid" value (e.g., Timer::clock_type::time_point::min()), it indicates that the timer has been shut down and should not perform any further operations.
Robust Cancellation with Shutdown Signalling
To handle expired timers gracefully, the cancellation logic can be modified to set the timer's expiration timepoint to this "invalid" value. This will signal the completion handler to stop future executions.
<code class="cpp">timer.get_io_service().post([]() { timer.expires_at(Timer::time_point::min()); });</code>
In the completion handler, the "invalid" timepoint can be checked to detect shutdown:
<code class="cpp">if (timer.expires_at() != Timer::time_point::min()) { // Continue normal operation... } else { std::cerr << "handle_timeout: detected shutdown\n"; }</code>
Conclusion
Cancelling basic_waitable_timer instances requires careful consideration of the timer's state. Detecting expired timers and signalling shutdown through a dedicated expiration timepoint allows for robust and predictable cancellation behavior.
The above is the detailed content of How to Safely Cancel Boost.Asio\'s basic_waitable_timer and Prevent Unexpected Behavior?. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undress AI Tool
Undress images for free

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

Yes, function overloading is a polymorphic form in C, specifically compile-time polymorphism. 1. Function overload allows multiple functions with the same name but different parameter lists. 2. The compiler decides which function to call at compile time based on the provided parameters. 3. Unlike runtime polymorphism, function overloading has no extra overhead at runtime, and is simple to implement but less flexible.

C has two main polymorphic types: compile-time polymorphism and run-time polymorphism. 1. Compilation-time polymorphism is implemented through function overloading and templates, providing high efficiency but may lead to code bloating. 2. Runtime polymorphism is implemented through virtual functions and inheritance, providing flexibility but performance overhead.

Yes, polymorphisms in C are very useful. 1) It provides flexibility to allow easy addition of new types; 2) promotes code reuse and reduces duplication; 3) simplifies maintenance, making the code easier to expand and adapt to changes. Despite performance and memory management challenges, its advantages are particularly significant in complex systems.

C destructorscanleadtoseveralcommonerrors.Toavoidthem:1)Preventdoubledeletionbysettingpointerstonullptrorusingsmartpointers.2)Handleexceptionsindestructorsbycatchingandloggingthem.3)Usevirtualdestructorsinbaseclassesforproperpolymorphicdestruction.4

People who study Python transfer to C The most direct confusion is: Why can't you write like Python? Because C, although the syntax is more complex, provides underlying control capabilities and performance advantages. 1. In terms of syntax structure, C uses curly braces {} instead of indentation to organize code blocks, and variable types must be explicitly declared; 2. In terms of type system and memory management, C does not have an automatic garbage collection mechanism, and needs to manually manage memory and pay attention to releasing resources. RAII technology can assist resource management; 3. In functions and class definitions, C needs to explicitly access modifiers, constructors and destructors, and supports advanced functions such as operator overloading; 4. In terms of standard libraries, STL provides powerful containers and algorithms, but needs to adapt to generic programming ideas; 5

Polymorphisms in C are divided into runtime polymorphisms and compile-time polymorphisms. 1. Runtime polymorphism is implemented through virtual functions, allowing the correct method to be called dynamically at runtime. 2. Compilation-time polymorphism is implemented through function overloading and templates, providing higher performance and flexibility.

C polymorphismincludescompile-time,runtime,andtemplatepolymorphism.1)Compile-timepolymorphismusesfunctionandoperatoroverloadingforefficiency.2)Runtimepolymorphismemploysvirtualfunctionsforflexibility.3)Templatepolymorphismenablesgenericprogrammingfo

C polymorphismisuniqueduetoitscombinationofcompile-timeandruntimepolymorphism,allowingforbothefficiencyandflexibility.Toharnessitspowerstylishly:1)Usesmartpointerslikestd::unique_ptrformemorymanagement,2)Ensurebaseclasseshavevirtualdestructors,3)Emp
